1. Field of the Invention
The present invention relates to the field of semiconductor manufacture, and particularly, to a method for cleaning a polishing pad.
2. Background of the Invention
Nowadays, phase-change memory technology is proposed as a new nonvolatile memory technology for new applications. The phase-change memory technology is superior to flash memory technology in many aspects, such as read/write speed, read/write frequency, data hold time, unit area and multilevel storage, and is a hot-spot of nonvolatile memory research currently. The technology of phase change memory makes sustainably progress to become more competitive in mainstream nonvolatile memory products.
An alloy solid phase-change material, for example a GST (e.g., Ge2Sb2T25) material that comprises Ge, Se and Sb, is employed in phase-change memory devices.
In prior art, the GST material is often patterned by etching. However, when critical dimension of the patterns decreases, the GST material can not be patterned as desired by etching. Chemical Mechanical Polishing (CMP) can be an advantageous solution.
A CMP apparatus typically comprises a head and a platen. A polishing pad is provided on the platen. During CMP, a device is fixed on the platen, and has a to be polished surface in physical contact with the platen and an opposite surface pressed downwardly by the head. Slurry is dispensed while the platen and the head respectively rotate during the process of polishing. Polishing speed is adjustable with down-force of the head and selectivity of the slurry. The slurry comprises chemical reagents, for example, SiO2, Al2O3, H2O2, BTA and/or the like. In general, before polishing another device, the polishing pad is cleaned with the slurry after polishing a device for removing residual byproducts.
FIGS. 1 and 2 are schematic cross-sectional views of a CMP apparatus for showing a conventional CMP process of polishing a GST material.
Referring to FIG. 1, a substrate 10 is provided. A dielectric layer 11 is formed on the substrate 10. An opening is defined in the dielectric layer 11, and is filled with GST material 12. The GST material 12 covers the dielectric layer 11 and serves as a phase change material layer for storing data. Referring to FIG. 2, the GST material 12 is polished by CMP to expose the dielectric layer 11. However, polishing the GST material device according to conventional art does not provide satisfactory performance.